1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that is equipped with a recording head for ejecting ink droplets.
2. Discussion of the Background
As an image forming apparatus, such as a printer, a facsimile machine, a plotter, or a multifunction machine including at least two of these functions, a liquid-ejecting image forming apparatus such as an inkjet recording device that uses a recording head for ejecting ink droplets is known. (It is to be noted that imaging, recording, and printing are synonymous with “image forming” in the descriptions below.)
There are two types of the liquid-ejecting image forming apparatus. A serial type image forming apparatus forms images using a recording head that ejects ink droplets while moving in a main scanning direction. A line type image forming apparatus forms images using a recording head that remains stationary while ejecting ink droplets. In either case, the liquid-ejecting image forming apparatus forms images by ejecting the ink droplets from the recording head onto a sheet of recording media while the sheet is being transported past the head. Therefore, transport characteristics of the image forming apparatus profoundly affect imaging performance.
Such a recording head, or liquid ejecting head, typically includes a compression chamber and an actuator for generating pressure to compress ink contained in the compression chamber, so that ink droplets are discharged from a nozzle connected to the compression chamber and onto the sheet.
As a pressure generating mechanism, the actuator itself may be of several types. There are known liquid ejecting heads that use a piezo-electric actuator composed of an appropriate piezo-electric element, a thermal actuator composed of a heating resistance member, and an electrostatic actuator that generates an electrostatic force. The actuator compresses individual liquid paths (hereinafter “compression chambers”) to eject the ink.
Currently, there is market demand for an image forming apparatus capable of outputting high-quality images at high speed. To accommodate such demand, at present, the size of the individual liquid droplets is reduced and/or the nozzles are packed more densely together on the recording head to provide the required high resolution. At the same time, to increase the speed of image formation, a driving frequency with which the liquid is ejected is enhanced and a long liquid ejecting head, such as a line-type head that includes more nozzles per head unit, is used.
To increase the number of nozzles by using a long liquid ejecting head, compression liquid members that form complicated liquid paths are often formed not of silicon, which is difficult and costly to work into long pieces, but metal plates or resins.
In particular, in one known approach, a vibration plate and a liquid path plate are simultaneously formed as a single multi-layered element (laminated material), in which multiple metal plates are connected with a single resin plate in advance.
However, connecting the individual metal layers together using adhesive requires many connection processes and high connection accuracy, which increases production costs and is susceptible to plate misalignment. Further, in general, a multi-layered configuration that requires connecting stainless steel plate with another material is not preferable because stainless steel is not easily adhered to other materials.
There is an additional difficulty. In the above-described approach, two metal materials that can be etched and which are located on both sides of an etching-resistant member are simultaneously etched, and thus interior partition walls of the liquid chambers (liquid paths) and convex portions (e.g. a connection portion) connecting to the piezo-electronic element are simultaneously formed. At this time, because the amounts of etching of the metal members that can be etched are adjusted by using materials having different speeds of etching, the thickness of members that can be etched needs to be calculated based on the etching rate, respectively. Therefore, getting dimensions and shapes that have sufficient quality for a liquid ejecting head is difficult.
Further, as described above, when the vibration plate is formed with the laminated material that includes the multiple metal plates connected with the resin plate in advance, one metal plate serves as a portion that forms the partition wall of the liquid chambers (an interior partition wall through liquid path), and the other metal plate serves as a portion that forms a connection portion connected with a driving mechanism (e.g. a piezo-electronic element).
Then, when one metal plate forms thick (higher) partition wall of the liquid chambers, it is preferable that the thin connection portion be formed in a shorter time than the other metal plate is even if the accuracy is relatively lower, and that, even if it takes a relatively long time, the connection portion connecting to piezo-electronic element be formed at high accuracy.